Kramer Industries Inc > Finishing Questions

Surface Finishing Questions

How do I pick a system to finish or deburr my parts?

Each type of deburring system has special characteristics. If you know the strong points of a system, you can select the most suitable system for a job. The most common options are:

Sandblasting Systems

Sandblasting propels abrasives at the part via a high-pressure air stream. It can abrade into the minutest details and produce a very even finish. The finish can range from a dull satin using abrasives or a bright satin using glass beads. Sandblasting removes small burrs but not heavy burrs (burrs which are too thick to bend or break off using a fingernail or pencil). Inexpensive manual systems as well as automated systems are available. Use sandblasting for light deburring or scale removal and to provide an even finish for painting or plating.

Barrel Tumbling Systems

Parts can be self-tumbled or tumbled with media. Tumbling is an aggressive system for heavy cutting with abrasives or for producing a shine with polishing media. Tumbling tends to attack edges and round corners more than other surfaces and does not penetrate into recesses well. Tumble parts to remove heavy burrs, round edges or create quick “safe edges” on stampings.

Vibratory Finishing Systems

Vibratory finishers shake parts and media at high speeds, causing the media to scrub the surface of the parts in an action similar to lapping. Since the parts and the media are moving at small increments on each stroke, the parts are not subject to severe stress or damage. Vibratory finishers produce very smooth surfaces, are safe for delicate parts, and have very good action inside recesses and holes. Vibratory finishing is the preferred choice for general deburring/finishing, deburring/finishing delicate parts and for precision deburring/finishing. Vibratory finishing is also safer for threaded parts, though it is not as good as barrel tumbling for rounding edges or removing tough, heavy burrs.

Which compound should I use?

The compound determines how the media will perform. Kramer’s 700 series powder compounds for barrel finishing systems and 1000 series of liquid compounds for vibratory finishing systems work best to protect metal from corrosion. To produce more shine and brightness, Kramer’s 900 series of powdered compounds for barrel finishing equipment or 2000 series liquid compounds for vibratory finishing equipment work best. Consult our compound selector guide for details.

Should I use ceramic or plastic media?

General burr removal can be performed using ceramic media. Ceramic media ranges from very hard for light deburring or polishing to softer media with more abrasive content for fast cutting. Plastic media is used when a part needs a good smooth surface finish, for delicate parts or when harder ceramic media would gouge a soft metal. Plastic media is considerably lighter than ceramic media so it will not distort a delicate part. Consult our Tumbling Media Selection Guide.

Why is my media wearing out so fast?

Ceramic burnishing media can lose 1% of its weight every eight operating hours. An aggressive cutting media can lose 1-2% of its weight every four operating hours. Plastic media will generally lose more than ceramic media due to its softer bond. Aggressive cutting media will wear out more rapidly than burnishing media due to the amount of abrasive added to the composition.

A compromise must be made between long life and fast cutting. Too little load in the machine causes a pounding action that greatly accelerates media wear; adding more media will smooth out the flow.

Why are my parts getting damaged?

Usually most damage is from one part hitting another. Generally, using too little media for the load damages parts. Try to maintain three parts media to one part of parts (by volume), which surrounds the parts in a matrix of media to prevent one part from hitting another.

Increasing the total load height will also help. A barrel tumbler should be run 50% full and a vibratory finisher 80-90% full for optimum cutting and a good finish. In a wet system, adding water will also soften the action.

Why do my parts get dark?

When parts are getting dark, it is usually a case of improper choice of compound or too little compound. Most Kramer compounds are formulated for use at a rate of 1-2 ounces per gallon of water. The ratio should be raised to 2-3 ounces per gallon if the solution is being re-circulated, providing extra chemicals to neutralize the higher load of residue. If the solution is being re-circulated, at some point it must be replaced so protection is not lost.

How do I handle waste products?

The wastewater from a deburring system is comprised of cleaning agents, solid residue from the media and particles abraded from the parts. Modern cleaning agents are biodegradable; however, the solids can harm the environment and clog pipes. The solids can be separated out using a gravity settling tank, a filter or a centrifuge. The gravity-settling tank is the least expensive option, but consumes the most space. Filter units and centrifuges take up much less space. Most small systems require only a settling tank and a pump to remove the usable water from the top of the tank.

Why are my parts warping?

Thin parts are sensitive to the compression stress load of glass beads. When blasting only one side, the parts will be unequally stressed and, therefore, warp. This can be avoided by blasting both sides of the part or by switching to an abrasive such as aluminum oxide that will scrub without imparting a compressive stress. It is also possible to minimize the effect by reducing the pressure.

Why is my barrel tumbler taking so long to process the parts?

It could be mechanical. The motor could be running slow due to age or a belt could be slipping. Loading the barrel past the 50% level also slows down the action. Adding too much compound can produce foam that will slow down the process. Adding more water can soften the action. Burrs may have increased due to worn tooling. Media may have worn down and no longer has the weight to do the cutting anymore. Using fresh media will speed up the cutting process.

Why is my vibratory finisher taking so long to process the parts?

The same rules apply as with barrel tumblers above. In addition, vibratory finishers are particularly sensitive to the water flow through the tub. Reducing the water flow will speed up the action.

Why is my sandblaster not producing finished parts as fast as it used to?

A worn nozzle will reduce the velocity of the abrasive, thus requiring more time to do the job. Replacing the nozzle will speed up the process.

The hose of nozzle may be clogged with a foreign object. Try passing a wire through the hose or nozzle to check.

Working too close to the part reduces the size of the blast pattern and pulverizes the abrasive, reducing its life. Blasting should be done at least six to eight inches from the part if using a suction blasting system and ten to fourteen inches away when using a direct pressure blasting system. Adding fresh abrasive to the machine without removing the old spent abrasive will make the operation very dusty and slow down the action of the fresh abrasive. When adding fresh abrasive, always remove the old material from the machine first. In a suction system there is an air jet behind the nozzle. If this is not replaced regularly, it will cause the air to deflect to one side and not accurately enter the center of the nozzle. This will eventually blast a hole through the side of the gun as well as slow the abrasive pick-up. Replace the air jet every two nozzles.

Operators often tend to hold the blast gun at a 90° angle to the work surface in hope that it will be more aggressive. However, this actually slows down the performance and pulverizes the abrasive. The gun should be held at a 30-45° angle to the work surface. This allows the abrasive to scrub the surface with the least abrasive wear.

If a visible stream of abrasive cannot be seen, one of the above conditions may apply or there may be a hole worn in the abrasive pick-up tube. Check the tube. The wrong blast material might be being used for the job. To remove material or scale, aluminum oxide is fastest. To remove scale and leave a shiny satin finish, glass beads are recommended, but it will take 40% longer than using aluminum oxide.

For additional information on finishing your parts, we’re just a phone call away.

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