Abrasives Lesson 7: Metalworking Belt Grinding Machines and Applications

by EMI Supply, Inc.
This article was published on Friday March 20, 2009.

Lesson 7

Metalworking Belt Grinding Machines and Applications

Part B
Centerless Grinding
 


Centerless Grinding



A centerless grinder grinds and polishes cylindrical objects without chucks or jigs to hold them during grinding. The primary elements of a coated abrasives centerless grinder are the contact wheel, the abrasive belt, regulating head, and the work rest blade. The workrest may incorporate suitable guides for leading the work to the wheels and other guides to lead it away, as well as proper means for supporting the work. The regulating head may have a wheel usually made of a rubber bonded abrasives or an abrasive belt. The regulating head imparts controlled rotation to the work, acting as a driving and braking element, and also supplies the work thru-feed through angular contact with the work. The thru-feed speed of the work depends upon the angle, together with the speed surface of the regulating head. A regulating belt offers two advantages - thru-feed speeds can be varied simply by changing the broad-angle or the speed, at the same time, maintaining line contact between the workpiece and regulating the belt. Changing the angle of a regulating wheel necessitates redressing it to maintain the line contact required to rotate and feed the workpiece properly. The use of a regulating belt running over a steel platen also makes it possible to tilt the head in either direction automatically, thereby reversing the direction of the feed and allowing multiple passes without removing the work from the machine. Nearly all centerless grinders are equipped for wet operation. On ferrous metal applications, straight cutting oils will produce the best results with the lowest unit costs. Soluble oils in rich concentrations (10:1, 20:1) are close behind straight oils in overall costs. Weak concentrations will markedly increase abrasive costs. A filter system for any coolant or lubricant other than expended water is strongly recommended.

On centerless work, success or failure of any job may often depend on the workrest blade. The blade must first of all be parallel with the machine both vertically and horizontally. The actual supporting surface must be smooth and free from galling. The angle, usually 30° from the horizontal, must be accurately machined.

Pressure on the blade increases with the degree of the angle and the length of the blade. Example - a setup that is correct for a 4" long blade may be too much angle for an 8" blade. When grinding large diameter work, the angle should be less than when using the same blade for grinding smaller diameter work. In other words, the larger the diameter of the piece to be ground, the smaller should be the angle of the blade. Blade material may be chilled iron, very hard alloys, or tungsten carbide. Aluminum bronze blades are especially well suited to grinding soft, ductile stringy materials. In polishing operations, nylon, plastics, and soft non-ferrous materials are used for workrest blades.

Most grinding is done slightly above the center to achieve roundness. For small work up to about 1" in diameter, a good rule is to adjust the blade vertically until the center of the work is above the wheel centers about 1/2 the working diameter. For larger work, the proportion is less, the above center adjustment rarely exceeding 1/2". Too much height will produce chatter which, in severe cases, will cause the work to jump out of the machine. When large heavy bar stock is being ground, below center grinding may be necessary because of the tendency of the work to whip.

Considerations in centerless grinding with coated abrasives:

1. Contact Wheels:

a. Minimum hardness usually 50A for polish. Typical hardness range 70A to 70D. Avoid metal contact wheels - not recommended.
b. Smooth face wheels often recommended for 1" diameter and under. A more aggressive wheel would reduce belt life.
c. Serrations are usually wide lands, narrow grooves. 1:2 ratio would be very aggressive - extreme recommendation. Very mild serration is sometimes advisable to keep the belt from floating (hydroplaning) on the contact wheel.

2. Contact Wheel Width-Belt Width:

a. Roughing - belt the same width as the wheel.
b. Finishing - belt narrower than wheel (1/4" to 1/2").

3. Tolerance Correction:

a. Triangulation - work not high enough above the center.
b. Undersized ends – contact wheel too soft.
c. Lead end undersized – guide misaligned.
d. Poor guide alignment – short pieces become barrel-shaped, spool-shaped, tapered.

4. Work Diameter – Stock Removal:

a. Stock removal per belt de-creases as work diameter decreases.
b. Stock removal rate decreases as work diameter decreases.
c. Reduce grit size to prevent stripping belts for maximum stock removal on small diameters.
d. Reduce grit size for harder to grind materials.

5. Feedmarks (Barber Poling):

a. Misalignment of guides. If the work guides at either the infeed or exit side crowd the work either forward or backward against the regulating roll, which can cause spiral marks and will also cause tapered grinding.
b. Outboard work supports or any method of work feeding that does not allow the work to enter and leave true and level with the workrest blade can cause spiral marks. Avoid tipping work up or down at either side.
c. Galling - use a blade of a harder material. Try a fluid with more lubricating quality.
d. Grinding pressure too high will also cause feed marks.

6. Set-up:

For maximum stock removal - back off infeed side of regulating wheel, relieve approximately 75% of diameter reduction.

7. Speeds:

5000 SFPM - general speed recommended - lower SFPM for heavier stock removal or low grindability material. In­crease SFPM for better finish or higher grindability material. 3500-6500 SFPM – roughing-finishing range. Lower SFPM for titanium.

Abrasive Considerations

Cylindrical contact between the work and belt produces a minimal area of contact and relatively high unit pressure or pressure per grit, even on light polishing operations. When high grinding pressures are used for heavy stock removal, pressure per grit can be very high. Consequently, contact wheels having less aggressiveness than normal are required for the best results.

Heavy-duty high perfor­mance products are required for all high-pressure heavy stock removal operations whether used wet or dry. High-performance general-purpose products usually produce best results for in­termediate and finishing operations. Standard duty general-purpose products are suitable for dry or oil operations for intermediate and polishing operations.

Rotary Table Machine

Rotary table machines permit one operator to load and unload workpieces that are processed on a continuous basis by multiple belt heads mounted outside the periphery of the table. There are three variations of this type in common use.

The first does flatwork on parts having a flat or nearly flat side to be polished. The work is placed flat side up on suitable fixtures to hold the work.

The table rotates slowly carrying the work under successive belt heads, usually through a grit sequence from rough to finish. The belt heads are modified hackstands that can be adjusted horizontally and vertically to position them over the work as it passes under the belt and contact wheel.

Most rotary operations are done dry, but it's also appropriate to use grease sticks for a belt lubricant, usually on the final one or two heads to produce a finer finish. Many parts are plated after polishing on rotary machines.

The second type is used for, work that is symmetrical in shape, such as toaster shells, sink faucet bases, etc. This is the type shown in Sketch 1. The work is loaded on fixtures that rotate the work in contact with the belt on a cam that follows the outline or profile of the part, the rotary table indexes the work successively from one belt head to the next and stops while at or to load and unload workpieces that are processed on a continuous basis by multiple belt heads mounted outside the periphery of the table. There are three variations of this type in common use. The belt head is automatically moved into contact and the work is rotated at that station.


Sketch 1



Belt heads can be positioned around the table as required so that they cover the entire workpiece tops, sides, and ends. The shape of the part determines whether the contact wheel face is flat or shaped. It is common to use both types to obtain complete coverage of the part.

A compact variation of the machine using shaped contact wheels for these applications is shown in Sketch 2.


Sketch 2



The third type is used for polishing and finishing work that is round, such as doorknobs, screwdriver shanks, bolsters on wood chisels, drift, and tapered punches, etc. The table indexes from one belt head to the next and stops while the fixture mounted parts rotate in contact with the belt.

Flat or shaped contact wheels or slack of belt or combinations of these can be used to obtain complete coverage of the work,

Abrasive Considerations

Grinding pressure levels on these operations are in the low to medium range. Abrasive belt specifications vary widely and depend on workpiece material and shape and flexibility requirements. Best belt life is usually obtained by using the least flexible belt that will successfully do the job.

Thru-Feed Machines

Except for the backstand grinder, thru-feed machines are the most common application of coated abrasive belts. As the thru-feed nomenclature implies, the workpiece is conveyed past one or more grinding heads that may grind the top, bottom, or both sides of the work. Thru-feed machines offer a big advantage over offhand work because of their high production rate. Tremendous savings in labor can be made with an accompanying increase in the uniformity of finish or size by changing from a hand operation to a thru-feed operation.

Thru-feed machines fall into two general categories pinch roll feed and conveyor feed. Pinch roll machines employ feed rolls before and after the grinding head to transport the work. They are used to rough and finish material in sheet form. The work is supported in the grind area by a "billy roll" opposing the contact roll. A disadvantage of the pinch roll type of thru-feed machine is that it cannot handle short workpieces. The minimum length piece that can be ground or polished is that equal to the distance bet­ween the in-feed and out-feed rolls.

Conveyor belt thru-feed machines carry the workpiece through the grind area on rubber or coated abrasive conveyor belt. The nominal minimum length of the work that can be ground is the distance between the hold-down rolls or shoes preceding and following the contact roll. However, shorter workpieces can be ground on a thru-feed conveyor machine by the use of soft rubber conveyor belts that hold the work by the depression in the rubber caused by the grinding pressure, by magnetic chucks for small ferrous parts, or by cleated or fixtured conveyor belts.



Belt widths on thru-feed machines range from 4" to 85" wide with 4", 6", 8", 10", 12", 15", 18", 24", 36", 42", 50" and 63" the nominal widths in general use.

Thru-feed machines may be wet or dry grinding operations, and some machines have cam arrangements to cause the grinding head to rise and fall to follow a contour such as the sides of open-end wrenches.

While the applications for thru-feed machines are endless, the type of work performed falls into three general categories – deburring, sizing, and finishing operations. Some examples are:

Deburring - computer parts, electric motor laminates, aircraft skins.

Sizing - clutch faces, file blanks, gun parts, brake shoes, open-end wrenches, terrazzo tile.

Finishing - saw blades, nameplates, stainless steel and trim, metal furniture parts, descale CR steel, automobile bumper blanks, vinyl floor tile.

Contact Rolls

The same fundamentals in contact wheel selection for backstand grinding apply to thru-feed machines. The roll hardness is generally dictated by the nature of the work to be accomplished, that is, whether it is a stock removal grinding operation requiring a hard wheel, or a finishing operation requiring a softer wheel.

The selection of face design is governed by the degree of aggressiveness that is required. For roughing, 63-60 to 70AR-12-45o are in general use and for finishing, 63-50 to 60AR-11 or 12-45° would be a general recommendation.

Two conditions affecting contact wheel selection on thru-feed conveyor machines that are not encountered on other coated abrasive applications are dubbing or cratering. Dubbing is the rounding off of the workpiece on the in-feed and out-feed ends and is caused by the contact wheel climbing up onto the leading edge and dropping off the trailing edge. All contact rolls will cause some dubbing; the degree depends on the roll hardness. Cratering is a similar effect around holes or cavities in the workpiece being more pronounced on the in-feed and out-feed ends than on the sides. Both conditions are related to contact wheel hardness. soft wheels aggravating the problem, and harder wheels minimizing the problem. Changing to smaller diameter contact rolls with their reduced area of contact is another mode of minimizing the problem of dubbing. Contact roll care on thru-feed finishing operations becomes a matter of vital importance frequently overlooked by customers. Damaged contact rolls will transfer the pattern to the workpiece, thus they should be repaired or replaced. Constant feeding of narrow workpieces through one area will cause uneven wear on the contact wheel as will changing from narrow to wide belts on the same roll. Periodic (weekly - monthly) redressing of the contact roll to maintain a straight roll parallel with the conveyor belt is strongly recommended, although often ignored. Tracking problems or the problem of wrinkled belts are often due to failure to dress the contact roll and/ or the idler pulley covering. The conveyor belt should receive the same consideration and be redressed periodically to assure a quality dimensioning or finishing operation.

Abrasive Considerations

On multiple head thru-feed machines, it is common practice to use more than one contact roll specification in the grit sequence. This in­variably employs harder, more aggressive rolls on the roughing end and softer, less aggressive ones on the finishing end for maximum effectiveness.

It may be equally appropriate to use more than one belt specification for the same reason, especially if the sequence covers a relatively wide range of grit sizes. Heavy-duty, high-performance products may be the best choice in grit sizes 80 and coarser where heavier stock removal is required with harder contact rolls and heavier grinding pressure.

Double Use of Belts

The finish produced by new belts is coarse and sharp but becomes finer with use. Where finish is critical, a fine uniform finish can be obtained by using a new belt of the final grit size on the next to last head for approximately one-half its normal life until the initial sharpness is removed. It is then moved to the last head where it will pro­duce a finer and more uniform finish. A new belt replaces its previous position in the line. The same thing can often be done with other grit sizes as well to reduce costs and the number of grit sizes used in a sequence.

Flex for Belts 13" and Wider

All cloth backings – single splice - 90 Flex

Sectional belts - S backings - T Flex

All paper backings – single splice - 45 Flex

All paper backings – section-al belts - 45 Flex

The specified flexes on cloth backings for wide belts minimize the possibility of creasing or folding of the belts due to adverse machine conditions or wear. The 45 flex on paper backings for wide belts provides shape stability of the belt and minimizes tracking problems.

Roll Grinding

Roll grinders are, basically, machines designed to use bonded wheels for reconditioning or truing large rolls. They are large machines and are similar to a lathe in that the work is mounted on centers and the grinding head is mounted on a carriage that travels on ways the same as the carriage on a lathe. The principal application for coated abrasives on roll grinders is in paper mills. Coated abrasives are not capable of the high grinding pressure, heavy stock removal; roll grinding done in steel mills. Three major makes of roll grinders are in general use Farrell-Birmingham, Lobdell, and Cincinnati.


Roll Grinding


Farrell-Birmingham machines are the most commonly manufactured machines that are originally equipped to use coated abrasive belts as well as bonded wheels (belts and wheels are rarely interchanged). Units are available to convert any make machine from a bonded wheel roll grinder to a coated abrasive belt grinder. A contact wheel is substituted for the grinding wheel, and an idler added to the tension and track the abrasive belt.

In paper mills, chilled iron rolls in the calender stacks become worn, burned or pitted and must be reground to restore the surface condition as well as close-tolerance in roundness and straightness. To produce a quality paper, .0005" is the maximum out-of-round or taper that can be tolerated. The conversion of a grinder from a bonded wheel to a coated belt machine offers a tremendous advantage in the reduction of grinding time. Although the abrasive cost will be increased, rolls can be ground with abrasive belts in about 1/3 the time required with grinding wheels. Because low horse-power motors are used (15 h.p.), the stock removal rate with two bonded wheels would be about .002"/hr. maximum whereas coated belts will readily remove .0067hr.

Roll grinding instructions and techniques are quite comprehensive and are covered by a separate Engineering Bulletin. The following are the basic considerations involved in roll grinding with coated abrasives:

1. Machine rigidity and over-all condition of the machine and grinder attachment must be good. The lack of rigidity or presence of wear in the base machine will produce a poor finish, poor accuracy, and shorter belt life. The degree of accuracy obtainable is equal to the accuracy possible with the basic machine and the accuracy obtainable when using grinding wheels.

2. It is absolutely necessary that the contact wheel run true. To ensure that the wheel runs true, it must be dressed after it has been mounted on the roll grinder spindle. All other things being in suitable condition, the dressing and balancing of the contact wheel is probably the most important single item.

3. The Type 91 contact wheel has been found to be the best for producing very close tolerances. It can also produce excellent finishes. However, unless the machine is in excellent condition, it is difficult to obtain a good finish with a Type 91 wheel. As a compromise for both roughing and finishing, a Type 81 70DR/60AR 14 or 15 contact wheel is suggested. This gives tolerances nearly as good as the Type 91 wheel, with considerably better finishes.

4. Belts for roughing and in­termediate work should be the same width as the con­tact wheel and the barber pole pattern disregarded. Belts for final finishing should be 1/2" narrower than the contact wheel and centered on the contact wheel. One or two passes will break in the belt so that the final passes will be free of barber pole or traverse marks.

5. A rule of thumb for determining if a grinding wheel application can be converted to belts is. When grinding chilled iron, if more than 5 or 6 h.p. per inch of wheel width is used, it is questionable whether the operation can be converted. The maximum practical pressure for coated abrasive use is approximately 4 h.p. per inch of belt width using a 70D hardness or Type 96 or 91 contact wheel. In some cases, the maximum can go up to 5 h.p. per inch when using 90A or softer contact wheels. 6. When close tolerances and/ or fine finishes are required, a flood of coolant on the work at the point of contact must be used.

Roll Grinding Attachments

Belt roll grinding attachments in different sizes are available to convert existing roll grinders or engine lathes to roll grinding with belts. These compact units are composed of a drive motor, spindle, contact wheel, idler and belt guard on a suitable mounting base. They are capable of producing the same accuracy as the base machine on which they are mounted.

Brush-Backed Sanding Wheels

Brush-backed sanding wheels are wheels made up with a series of brushes, not unlike paintbrushes that back up shredded abrasive strips They are used for polishing contoured workpieces and are available in 6-8-12-16 and 32 brush models in 1", 2" 2-1/2", 4" and 6" widths, and diameters ranging from 4-3/4" to 16". The smaller diameter wheels are suited for use on portable equipment, and the large ones on conventional lathes. These sanding wheels all store multiple strips of coated abrasives within the frame and provide a means of feeding these strips so that they will extend the desired length beyond the tips of the brushes. Loadings are available in a wide variety of grades. The aggressiveness or finished quality attainable with these wheels can be controlled by the selection of grades, selection of brushes, or, on some machines, by control of the operating speed.


Brush-Backed Sanding Wheels


These wheels are particularly good on contoured work. The brushes force the coated abrasive into and around corners, hollow and fluted surfaces, and small openings. Fairly coarse abrasives can often be used to obtain fine satin finishes.

Considerations in the use of brush-backed sanders:

1. Presswork from 1/2" to 5/8" into the face of the head for best results. Greater pressure will neither improve finish nor speed the process. Excessive pressures wear out loadings and brushes needlessly.

2. These heads are designed primarily for finishing operations. Do not attempt to accomplish stock removal operations with them. They may be used to remove light scale or burrs.

3. Backings and abrasives for loadings should be selected to meet the requirements of the material being finished.

4. Most frequently used grits in the metalworking and plastics fields range from 120 to 320, in woodworking applications from 80 to 120. Grits 80 and coarser give relatively short life and should not be recommended.

5. Two types of shredding (longitudinal slits) are available - straight shred and staggered shred - each ordered by CP number. The straight shred is generally used for woodworking and the staggered shred for metalworking.

6. Principal manufacture of brush-backed sanding wheels:

a. Vonnegut Heads - Grinding and Polishing Machinery Corp., Post Office Box 19038, 2801 Tobey Drive, Indianapolis, IN 46219.
b. Sand-O-Flex Wheels - Merit Abrasive Products Inc., 201 W. Manville. Compton, CA 90224.

Flap Wheels

Flap wheels are strips of abrasive radially mounted with the inner ends permanently fastened to a hub to form a wheel.

They have a reasonable degree of flexibility and are used for deburring stampings and machined surfaces, polishing and blending a wide variety of ferrous and non-ferrous metals as well as plastics and other non-metallics. They can be shaped to conform to the contours on a part.

They are available in sizes from 1-10" in diameter up to 2" wide. The smaller diameters are usually used on portable equipment and the larger sizes on bench or floor stand lathes.

Flap wheels are suitable for finishing operations only. They are not appropriate for heavy stock removal. They should be used with light pressure so that the tips of the flaps do the work. The use of heavier pressure will only wear the wheel out prematurely with little increase in the cut.

The most commonly used grit sizes are 60, 80, and 120 although finer grit sizes are used for some finishing operations. Resin bond X weight products are usually preferred for longer life and lower costs over glue bond J weight products.


Flap Wheel

 

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Production Selection Guide - Metalworking

 

Round Work - Centerless Grinders (Belt width 12" and Under)

Grit flange

Wet Dry

Carbon Steel

Stainless Steel

Aluminum Brass

Titanium
Zirconium

Flex

Splice

Roughing
24 - 60

Wet or Dry

A-X1180, A-Y1186
A-Y1386, A-X880H

A-X1180, A-Y1186 A-X880H, A-Y1386

C-X980H, A-X880H A-X780F

A-X1180, A-Y1386 C-X980H, C-X965F

45
45

CB
CB
 
Dry

A-X1180. A-X880H
A-X865F, A-X875F

A-X1180. A-X880H A-X875F, A-X865F

A-X880H. C-X875F A-X780F

A-X1180, C-X875F C-Y879F

45
45

CB
CB

Intermediate 80 - 150

Wet or Dry

A-X880H, A-X780F
-

A-X880K A-X780F
-

C-X980H. A-X880H A-X780F

C-X980H, C-X965F
-

45
45

CB
CB
 
Dry

A-X880H, A-X780F
A-X875F, A-X770F

A-X880H, A-X780F A-X875F, A-X770F

A-X880H, C-X875F A-X780F

C-X875F, C-Y879F
-

45
45

CB
CB

Finishing
180 - 320

Wet or Dry

A-X965F, K-X945E
-

A-X965F, K-X945E
-

C-X965F, A-X965F
-

C-X965F, K-X945E
-

45
-

CB
-
 
Dry

A-X875F, A-X770F
-

A-X875F, A-X770F
-

C-X875F. A-X770F
-

C-X875F
-

45
-

CB
-
 

Round Work - Roll Grinders (Belt width 12" and under)

Grit Range

Wet

Carbon Steel
Cast Iron

Stainless
Steel

Aluminum
Brass

Chilled
Iron

Flex

Splice

Roughing
24 - 60

Wet

A-Y1386, A-Y1186
A-X1180, A-X880H

A-Y1186, A-X1180
A-X880H, A-X780F

C-X980H, C-X965F
-

C-X980H.C-X965F
-

45
45

CB
CB

Intermediate 80 - 150

Wet

A-X880H, A-X780F
-

A-X880H, A-X780F
-

C-X980H, C-X965F
-

C-X980H,C-X965F
-

45
-

CB
-

Finishing
180 - 320

Wet

A-X965F, K-X945E
-

A-X965F, K-X945E
-

C-X965F
-

C-X965F, K-X945E
-

45
-

CB
-
 

Flat Work - Narrow Belt (12" & under)
Thru-feed Grinders & Polishers

Grit Range

Wet Dry

Carbon Steel
Cast Iron

Stainless Steel Hi Nickel Alloys

Alum. Brass
Non-Ferrous

Titanium
Zirconium

Flex

Splice

Rough­ing
24
-60

Wet or Dry

A-Y1386, A-Y1186 A-X880H, A-X780F

A-Y1186, A-X1180
A-X880H, A-Y1386

C-X980H, A-X1180
A-X880H, A-X780F

C-X980H, C-X965F
-

45
45

CB
CB

Dry

A-Y1386, A-Y1186 A-X875F, A-X865F

A-Y1186, A-X880H
A-X875F, A-X865F

A-X880H, A-X770F
A-X827F. C-X875F

C-X875F, C-Y879F
-

45
45

CB
CB

Inter­medi­ate 80 -150

Wet or Dry

A-X880H, A-X780F
-

A-X880H, A-X780F
-

C-X980H, A-X880H
A-X780F

C-X980H, C-X965F
-

45
45

CB
CB

Dry

A-X880H, A-X770F A-X780F, A-X875F

A-X880H, A-X770F
A-X875F, A-X780F

A-X880H, A-X770F
A-X827F, C-X875F

C-X875F, C-Y879F
-

45
45

CB
CB

Finish­ing
180 -320

Wet or Dry

A-X780F, A-X965F K-X945E

A-X780F, A-X965F
C-X965F

C-X980H. C-X965F
-

C-X980H, C-X965F
-

45
45

CB
CB

Dry

A-X770F, A-X875F
-

A-X770F, A-X875F
C-X875F

A-X770F, C-X875F
-

C-X875F
-

45
45

CB
CB
 

Flat Work - Wide Belt (Over 12")
Grinders & Polishers

Grit Range

Wet
Dry

Carbon
Steel

Stainless
Steel

Aluminum
Brass

Titanium
Zirconium

Flex

Splice

Rou
gh
ing
24 –
60

Wet or Dry

A-X1180, A-X880H A-Y1186

A-X1180. A-X880H A-Y1186

A-X1180, C-X980H
-

C-X980H, C-X965F
-

90
90

CB
CB

Dry

A-X1180, A-X880H
A-X875F
A-E655F

A-X1180, A-X880H
A-X875F
A-E655F

C-X875F, A-X827F
-
-

C-X875F
-
-

90
90
45

CB
CB
NTS

Inter­
medi-
ate
80 –
150

Wet or Dry

A-X880H, A-X965F C-X980H

A-X880H, A-X965F C-X980H

C-X980H, A-X880H
-

C-X980H, C-X965F
-

90
90

CB
CB

Dry

A-X880H, A-X875F
A-E655F
C-X875F

A-X880H, A-X875F
A-E655F
C-X875F

A-X827F, C-X875F A-E675F, A-W678F
-

C-X875F
-
-

90
45
90

CB
NTS
CB

Finish
ing 180
- 320

Wet or Dry

A-X965F, C-X965F K-X945E

A-X965F, C-X965F K-X945E

C-X980H, C-X965F
-

C-X980H, C-X965F K-X945E

90
90

CB
CB

Dry

A-X875F, C-X875F

A-X875F, C-X875F

C-X875F

C-X875F

90

CB
 

Brush Backed Sanding Wheels
 

Carbon Steel Stainless Steel

Aluminum, Brass, Non-Ferrous

A-X770F, A-X965F

A-X770F, C-X965F

 
 

Flap Wheels
 

Carbon Steel Stainless Steel

Aluminum, Brass, Non-Ferrous

A-X770F, A-X875F

A-X770F, C-X875F
 

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Question on Lesson 7

1. In centerless grinding, the regulating head:
a. determines the accuracy obtained
b. imparts controlled rotation to the work, acting as a driving and braking element
c. determines both accuracy and finish obtained

2. Rotary table and thru-feed machines are both capable of high production rates. An advantage of the rotary system is:
a. one operator can load and unload the work
b. very high grinding pressures are typically used for heavy stock removal
c. a circular scratch pattern is desirable for some work

3. Critical finish requirements on multiple head thru-feed operations can often be most easily met by:
a. using the finest grit size practical for the material being finished
b. reduce feed rate so that the work has more contact time with the belt
c. advancing finishing belts at half-life to the last head

4. For maximum efficiency on multiple head thru-feed operations:
a. belt speed is of critical importance
b. it is often appropriate to use more than one belt and contact roll spec in the sequence
c. grinding pressure must be maintained at a constant level

5. Flex tor belts 13" and wider should be:
a. 90 flex for all single splice cloth backings
b. 45 flex for all single splice paper backings
c. both of the above

Courtesy Carborundum Abrasives

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