ESP Marketing (UK) Ltd
3 Boleness Road
Telephone: 01945 580980
Fax: 01945 466549
19 Silver Street, WITCHAM, Cambs. CB6 2LF
Tel: 01353 777305 Fax: 01353 777848
|ESP Barrel Lacquering Lines|
Barrel Finishing as cheap easy method fro
coating component parts.
ESP have recently completed the design, manufacture and installation of a small twin barreling
plant for coating turned hardwood parts such as knobs and keyrings.
The machine is a parallel, rear drive, twin roller mounted onto box steel frame with two barrel
capacity and takes up floor space of 2 x 1 metres with the option to add further capacity. The
barrels fitted within large side wheels run on small diameter rollers which reduce RPM which is
precisely adjusted by an electronic speed controller and a reduction pulley from motor to roller. A
timer is used so that once initial experimentation in terms of numbers of items, lacquer/stain
addition and running time against speed had been determined repeatability is effected.
The octagonal barrels are made from MDF with two/four inner paddles fitted & angled to the
direction of run with good through ventilation holes. The barrel is filled and emptied via an easy
opening & securely locked 'door'.
As a method of coating it is very simple and cheap however certain elements have to be observed
to ensure good results.
1) Temperature should be at 20 degrees and above
2) The addition of finishing materials must be kept to a minimum to maintain speed of dry and
help to achieve sheen levels. Faster drying equals higher sheen.
3) Loading the barrel correctly is critical in achieving fast throughput. Overloading reduces
speed of dry and results in matt sheen levels and severely reduced production
4) Loading with clean parts is essential to avoid bits and discolouration from wood dust
5) Parts for recoating need to be rested and unloaded to allow excess solvent to
evaporate and for the lacquer to harden off to resist any solvent attack before applying
further coats. Use trays which allow air to pass through them freely.
6) Running the barrel does not achieve faster drying but could damage the products.
7) The addition of small shapes to the parts mix assists the coating of items which cannot
make total surface contact with each other
8) Single component N/C lacquers give best results
The following information has been lifted from various articles published in wood working/finishing
Priming and Finishing by Tumbling or Barreling April 1997
When an article has a shape which is difficult to attach to dipping jigs, is too small in size or is
manufactured in very large quantities, it can sometimes be primed, sealed or finished by tumbling
or barreling. For wooden articles the tumbling barrel is usually octagonal and mounted to rotate
horizontally at speeds varying from 25 - 45 r.p.m.; the quick release lid and two of the sides are
pierced by numerous holes to facilitate the evaporation of solvent and the drying of the article.
The barrel is half or two-thirds filled with articles, a calculated quantity of sealer, stain or tumbling
lacquer is poured on, the lid clamped down and the tumbler started. After 25 - 45 mins the articles
are smooth, dry and ready for unloading.
Excess paint causes unsightly fat edges and very slow drying. Where the quantity of paint has
not been established by trial, a basis of one gallon of cellulose finish to 300 sq ft of surface to be
covered should be employed, but it is best to tumble the articles with a little less than this
amount for 5 min, adding the remainder if they are not covered.
An example can be quoted, in which an experiment of two gross of 6 in. long wooden paint brush
handles were tumbled with cellulose synthetic sealer. Each handle had a surface area of 6 sq in.
and the total area of the two gross was 12 sq ft; the calculated amount of sealer was about one
third of a pint. One quarter of a pint of sealer was poured on to the articles which were tumbled
for l0 min and, on inspection, were found to be covered. They were then re-tumbled for a further
15mins, after which they were found to be evenly coated, smooth and dry and ready for either
spraying or dipping in the finishing coat.
There are many types of tumbling barrels; some in the United States have hollow shafts with
facilities for blowing in hot air to accelerate the drying. In the United Kingdom barrels mounted
on eccentric shafts have been employed to give a reciprocating as well as a circular motion to the
load. They can be upto 10ft long with open ends, the bottom half of each end being shielded by
a wooden partition which is stationary at about žin. from the circular edge of the rotating barrel;
thus a load of 200 gross of brush handles would be retained in the bottom of the barrel, rotating
over one another and spreading 2 gallon of sealer until dry. One company recently made several
barrels on eccentric shafts to seal all the dowels, legs and rails of their products, thus saving over
80 per cent of the sealing lacquer and 95 per cent of the labour employed in spraying and
The viscosities of tumbling cellulose materials vary from 40 - 90 sec, Ford No. 4 cup. Spirit or
oil stains may be lower than this, but viscosities higher than 90 sec are likely to cause sticking
and imperfect spreading. The sound made by the articles being tumbled will reveal whether they
are rotating freely or sticking.
Toy blocks are often tumbled first with non-toxic spirit stains lightly bound in shellac, then re-
tumbled with hard balls of wax composition to obtain the required sheen. Pigmented, tumbling
enamels, often based on shellac, can contain two or three times the normal quantity of pigment in
order to get adequate cover on edges and corners; these give only a satin or semi-matt sheen,
but the gloss can be increased by tumbling again with hard wax.
Tumbling is severely restricted by the size and shape of articles; if these are very heavy they
cause extensive bruising of the surfaces, and if they are unsuitably shaped they will not smooth
the surfaces of each other and the paint will not reach all crevices or cover exposed surfaces
Tumbling (second opinion)
The 'tumbling' method of finishing is eminently suitable for the coating of small wood, metal or
plastic workpieces which would present handling problems by conventional spraying or dipping
methods. In its particular field of application, the process offers distinct advantages, because
articles can be bulk-finished with the minimum of coating material and handling.
The equipment required is relatively simple in design, consisting essentially of hardwood or steel
tumbling barrels of various sizes. These are round (with internal baffles) or polygonal in cross-
section and in operation are rotated horizontally, vertically or obliquely. Often a combination of
different motions is adopted. The basic principle of tumbling is that the workpieces cascade while
the barrel is in motion. The continuous movement thus provided eventually ensures that the
coating material is uniformly distributed over the entire surface of the work. Successfu1 tumbling
depends on the strict control of the variables i.e. the quantity and surface area of work inserted,
the quantity, viscosity and wetting characteristics of the coating material, the speed of the
barrel and the duration of the tumbling period. The balance is often critical and initially a certain
amount of investigation is necessary to determine optimum conditions; for example, too high a
speed will cause the entire charge to be flung outwards by centrifugal force.
The barrels are loaded with the work to approximately one third capacity, the measured quantity
of coating material is added, and the barrels are rotated at approximately 30 r.p.m. for the period
necessary to ensure overall coverage. This period varies with the type of work, but 30 min is
common. For processing flat pieces that may tend to nest or interlock, corks, wooden beads or
circular objects are inserted to ensure separation of the parts. The work is finally emptied on to
wire mesh trays for air drying or stoving as required.
The process is applicable to all conventional types of coating materials. Features of the coating
formulation are good build or film forming properties, coupled with high hiding power in the case
of coloured finishes; often a small percentage of a lubricating agent is incorporated to provide the
necessary 'slip', whilst working viscosities are generally higher than those for spraying and
dipping. The paint should have quick setting properties, and it is usual to apply several thin coats
in order to achieve the desired 'build'.
ESP Marketing (UK) Ltd
3 Boleness Road
Telephone: 01945 580980
Fax: 01945 466549